Central cyanosis reflects systemic hypoxia. It may be seen in patients with congenital cyanotic heart disease or acute hypoxia from pulmonary oedema,where it indicates impending death. Look for a bluish discoloration of the lips and tongue. The sensitivity of the finding reflects the level of the plasma hemoglobin, or more specifically the plasma concentration of deoxyhaemoglobin in peripheral blood. In a patient with a normal hemoglobin (13.5-18 g/dL in men, 11.5-16 g/dL in women) central cyanosis becomes detectable with oxygen saturation values of between 80 and 87 %. Anaemic patients require more severe hypoxia before cyanosis becomes clinically apparent. With a hemoglobin of 6 g/dL oxygen saturation would need to fall as low as 60% before cyanosis becomes clinically apparent.